Brake force transmission device for a brake force amplifier

ABSTRACT

The invention relates to a brake force transmission device for a brake force amplifier with an elastic reaction element ( 7 ), an input body ( 22 ), with an associated working surface (d 4 ), an output body ( 24 ), with an associated working surface (d 4 ), with a first transfer ratio, defined by a working surface ratio, actively dependent on the reaction element ( 7 ). The aim of the invention is to provide a means, of simple construction, where possible arranged in the form of an assembly, which gives the driver of a motor vehicle increased support when high braking force is required. According to the invention, means ( 2,4, 6,11 ) are provided, which reduce the reaction force supplied to the input body ( 22 ) by a certain proportion, after a certain pressure in the reaction element ( 7 ). The driver is thus given additional support and a relatively reduced increase in input force is required for a further increase in output force. It is thus possible for the driver to better control the necessarily higher braking forces after the discrete increase in the ratio of the amplification.

[0001] The present invention relates to a brake force transmissiondevice for a brake force booster with an elastic reaction element, aninput member with an associated effective surface, an output member withan associated effective surface, and with a first transmission ratiodefined by a ratio of the effective surfaces being in operativeengagement with the reaction element.

[0002] Japanese utility model Sho 61-205858 e.g. discloses atransmission device of this type. The transmission device comprises aresiliently preloaded, moveable pressure member (38 b) arranged on aninlet side (or an outlet side) and causing an abrupt increase of theboosting ratio due to a change of the surface ratio on the inlet side(or on the outlet side), with an input force predetermined.

[0003] In view of the above, the present invention is based on atransmission device of the type to be taken from the preamble ofclaim 1. It is an object of the invention to provide a transmissiondevice that has a particularly small overall size and is easy tointegrate into a standard type of brake force booster. Consequently, anobjective is to permit employing the transmission device as desired alsoin already existing brake force boosters, without necessitating costlynew constructions or modifications.

[0004] This object is achieved by the combination of features to betaken from the characterizing portion of claim 1.

[0005] In the solution of claim 1, the invention principally involvesthat deformation of the reaction element displaces the switching ring inopposition to the force of the spring towards the input member until thesurface of the reaction element reacting on the control housing isincreased by the annular surface of the switching ring. The result is asmaller effective surface at the input and, thus, also an increase ofthe transmission ratio of forces. More specifically, this means thatafter the switching ring has moved into abutment on the control housing,the reaction of the output member applied to the input member isreduced. Thus, the driver can reach the same braking effect, with areduced pedal force.

[0006] A particularly simple design for the transmission device isachieved in an improvement of the invention by the combination offeatures of claim 2. The spring assembly may have a very simple design,as will be explained in the following. Further, the spring assembly mayform a closed construction unit that is integrally inserted into thecontrol housing when the brake force booster is assembled. The sameapplies to the switching ring that may be connected integrally to thespring assembly, yet forms a separate unit in an advantageous manner.The advantage of these measures in particular resides in the fact thatboth the spring assembly and the switching ring may be kept on stock indifferent types, and the control housing may then be equipped with themdepending on the requirement and the desired course of boosting.

[0007] In a favorable improvement of the invention, it is advisable touse the features indicated in claim 3 with respect to the springassembly. Essentially, the spring assembly may have a symmetricaldesign. It is only important in this regard that the two retainingelements can be displaced relative to each other in opposition to theforce of the spring. Further, the stop element ensures that the tworetaining elements are combined in a unit and none of the retainingelements can get lost. Besides, it is possible to clearly define theforce with which the two retaining elements are preloaded towards eachother by selecting the spring and the distance between the two retainingelements.

[0008] In accordance with the combination of features as in claim 4, thefirst retaining element can make catch directly on the reaction elementby way of a projection that reaches through the second retainingelement. It is, however, also feasible that the first retaining elementacts on the reaction element only indirectly by way of a pressuremember. This is advantageous inasmuch as the pressure member may bechosen corresponding to the variation of the desired amplification. Asit is also possible to select the switching ring that can be insertedseparately, as has been explained hereinabove, the combination of theswitching ring and a pressure member permits largely varying the courseof the characteristic curve of amplification. Thus, the boostingperformance of the brake force booster can be adapted to a great extentto the respective requirements by the selection of the switching ring,the pressure member, and the spring element in dependence on the inputforce. It is also favorable that the mentioned elements may beretrofitted and thus allow an adaptation of the booster already inseries production.

[0009] The features according to claim 5 describe as an improvement ofthe invention a particularly simple possibility of guiding the switchingring within the housing. In this arrangement, the switching ring withits inside surface may be guided both by way of the outside surface ofthe projection and by way of its outside peripheral surface on theinside peripheral surface of a projection on the control housing.However, only guiding of the switching ring on its outside peripheralsurface is possible for the case that the first retaining element makescatch at the reaction element only indirectly by way of a pressuremember.

[0010] In accordance with the combination of features in claim 6 it maybe advisable that the switching ring abuts on the control housing and,thus, changes the characteristic curve of amplification. The featuresdisclosed in claim 11 permit achieving a still simplified construction.In this arrangement, the switching ring does not abut directly on thecontrol housing but indirectly by way of the second retaining element onwhich it is acting. This permits a very simple configuration of theswitching ring, hence, it is made of a simple cylindrical ring. Further,a large stop surface may be achieved in a very simple fashion by thedesign according to claim 11 because the second retaining element anywaymust have a sufficiently large extension in a radial direction foraccommodating a sufficiently large spring.

[0011] The combination of features of claim 7 also permits achieving asimplified manufacture. Because the fixed ring may additionally be usedas a guide for the switching ring, the strength of the switching ringand thus the course of the characteristic curve of the amplification maybe influenced by correspondingly dimensioning the inside recess of thefixed ring and the outside diameter of the switching ring.

[0012] The provisions in claim 8 allow achieving further simplificationfor the design of the transmission device of the invention. The controlhousing serves for axially guiding the second retaining element andadditionally as a stop. Thus, the walls of the guiding grooves areutilized twice because they are used for guiding in a longitudinaldirection and as a stop.

[0013] To achieve a sufficient degree of spring force despite smalldimensions, the combination of features as disclosed in claim 9 isadvisable in an improvement of the invention. The spring may influencethe course of the characteristic curve of amplification by acorresponding selection of the characteristic curve of the spring. Theprojection may be integrally connected directly to the first retainingelement corresponding to the features of claim 10. The retaining elementmay also be riveted to the projection for saving material and for thesuitable combination of construction materials.

[0014] It is an important aspect for the invention that it is integratedinto a controlled brake system in an especially appropriate manner, asis explained in connection with claim 11. This applies in particularwhen in the controlled brake system the distribution of the brake forcesto the individual wheels or wheel groups is controlled in dependence onthe slip at the respective wheel or the wheels. It is thereby renderedpossible with low effort that a sufficiently high amount of brakepressure can be generated even if a driver actuates the brake with a tooweak depression of the pedal. On the other hand, the controlleddistribution of brake forces ensures that the vehicle will not leavetrack as a result of slip on one or more wheels.

[0015] The advantage of the invention is basically due to the followingfacts. The present function principle essentially and simply relates toa biased spring that is interposed between the valve piston and thepiston in an axial function. Functionally required stops are provided,with a direct transmission being ensured when the booster is operated.The preferred constructive features are as follows: There is provisionof a compression spring that is captivated in a straightforward fashion,and a very simply designed spring element is used. The control housingincludes a fixed ring that is configured very simply as a disc taking upforce. This fixed ring can move to abut on the end surface of a steppedbore in the control housing, with grooves being indented into the wallof the stepped bore that serve for guiding and as a stop at the sametime. In other words, the following features are especially important inthe construction described herein.

[0016] The present function principle is basically and simply related toa preloaded spring that is interposed between the valve piston and theannular piston in an axial function, with some functionally inducedstops, with a direct force transmission being ensured during operation.Construction features to be especially emphasized are thestraightforwardly captivated compression spring(s) (5), an inexpensiveforce-transmission member. A control housing area (4) behind the disc(1) taking up forces receives multi-functionally the forces of theswitching ring (2) and additionally serves for guiding a stop plate assecond retaining element (6) with stop. The stop plate (6) biases thespring, conducts the reaction forces of the annular piston (2) to thespring, represents the stop of the annular piston as well as atransmission member during operation.

[0017] The invention is especially efficient in connection with anelectronically controlled brake force distribution because in the eventof failure of the ABS (anti-lock system) usually also the electronicbrake force distribution (EDB) will fail. In this case, the driver canstill properly dose the brake pressure in the steep branch of thebooster characteristic curve. This is in contrast to systems with apanic braking function such as a brake assistant (BA) or mechanicalbrake assistant (MBA) which are considerably more difficult to masterduring change-over to an infinite (steep) characteristic curve of brakeforce boosting.

[0018] Two embodiments of the present invention will be explained in thefollowing by way of the accompanying drawings. In the drawings,

[0019]FIG. 1 shows a first embodiment of a transmission device of theinvention in cross-section and a broken-out illustration.

[0020]FIG. 2 is a broken-out cross-sectional view of the embodiment ofFIG. 1 at the level of the line of intersection A-A in FIG. 1.

[0021]FIG. 3 shows a second embodiment of the invention.

[0022] The design and the function of the transmission device 1 will bedescribed in detail in the following, and the basic function of a brakeforce booster as disclosed exemplarily in PCT/EP98/07314 is assumed asbeing known.

[0023] In an idealized view, brake force boosters principally known inthe art have a constant transmission ratio over the entire operatingrange up to the so-called point of maximum boosting, with the producedoutput force (pedal force and boosting force) rising linearly above theinput force (pedal force). In principle, the transmission ratioessentially influencing the pedal feeling of the driver is defined bythe ratio of the effective surface (d4) associated with the outputmember to the effective surface (d3) associated with the input member.For greater braking effects, that means, at a higher brake force level,it is considered positive to support the driver to a stronger degree.More specifically, a higher transmission ratio is caused, as can betaken e.g. from JP-Sho-61-205858.

[0024] In addition to other parts to be assigned to the brake forcebooster, which do not have any major influence and therefore will not bedescribed in the following, a transmission device 20 of the inventioncomprises an input member 22 with a valve piston 23, said input memberbeing movably arranged in a control housing 8 with a first sealing seat21, as well as an output member 24 for actuating a master brake cylinder(not shown). Interposed between the input member 22 and the outputmember 24 is a preferably disc-shaped elastic element 7 which is made ofplastic material or rubber material and is encompassed on all sides bysurfaces of parts of the transmission device 20, in other words, isquasi encapsulated between movable walls. When pressurized the elasticreaction element 7 behaves like an incompressible fluid according to thelaws of constancy of volume and acts quasi as a mediator between thepedal forces introduced by way of the input member 22 and the brakereaction forces which are fed back from the vehicle brake system to thevehicle operator. Consequently, balanced forces prevail at the reactionelement 7 in each position of brake actuation.

[0025] The reaction element 7 is seated in a bowl 25 that is open to theleft in FIG. 1 and is formed by a first bore 26 in control housing 8 anda fixed ring 1 that is supported at edge 28 of a second bore 27 of thecontrol housing 8. The bowl has an inlet opening 29, wherein the frontend of the output member 24 in the drawing is guided. Said output member24 at its right-hand end in FIG. 1 passes over into a plate 10 thatcloses the bowl 25 and bears against the wall of the reaction element 7that points to the left in FIG. 1. Towards the right hand, the reactionelement 7 is supported on the fixed ring 1 which, in turn, abuts on thecircumferential edge 28 or step between the first bore 26 and the secondbore 27. The surface for the plate 10 is indicated by value d4. Thefixed ring 1 has an opening inside that is indicated by the value d3 asarea of the opening. In opening (d3) a switching ring 2 is guided whichis moveable relative to the fixed ring 1 in the longitudinal directionof the booster. A spring element is composed of a first retainingelement 3, a second retaining element 6 and a spring 5. Said spring 5preloads the two retaining elements 3 and 6 in relation to each other sothat they can only be displaced against each other with a defined force.The maximum distance of the two retaining elements is determined by astop 12 that is arranged at a projection 13 of the first retainingelement 3.

[0026] The first retaining element 3 is furnished with projection 13which can be configured as one single continuous piece along with theretaining element. However, it is also suitable to design the projection13 as a rivet part, as illustrated in FIG. 1. To this end, the rivetpart may be made of a material with appropriate strength, while thefirst retaining element 3 is made of a formable metal sheet. At the endof the rivet part 13, stop 12 is provided that is configured as acircumferential nose. It is ensured by this stop that the secondretaining element 6 can move only a predetermined distance away from thefirst retaining element 3. The projection 13 may project until into theinterior of the switching ring 2. As in the present embodiment, however,the rivet part 13 may also be succeeded by a pressure member 31, whichextends through the switching ring 2 and acts on the reaction element 7.

[0027] Guiding the second retaining element 6 in the control housing 8is important for the present invention. This guiding arrangement iseffected by means of guiding grooves 4 which are machined into theinside peripheral surface of the second bore 27, distributed over theperiphery of said bore. For guiding purposes, the second retainingelement 6 includes correspondingly designed guiding projections 15 thatengage into the grooves 4, as shown in FIG. 2. An end wall 11 in eachgroove forms a stop for the guiding projections 15 so that when theguiding projections 15 abut on the respective end wall 11, a forcedirected to the right to the second retaining element 6 in FIG. 1 istaken up by the control housing 8. All other components illustrated inFIG. 1 are not essential for the present invention and will not bedescribed more closely herein.

[0028] The mode of operation according to the embodiment of FIG. 1 is asfollows. When the input member 22 in FIG. 1 is displaced to the left inthe position shown in FIG. 1, the pressure member 31 and the switchingring 2 will make catch at the reaction element 7. This renders a surfaced3 active at the reaction element 7, while the reaction element 7 actswith surface d4 towards the output member 24. The ratio of these twosurfaces defines the boosting ratio of the booster in this operatingcondition. The switching ring and pressure member 31 then move togetherin parallel because the spring 5 is so stiff that it will not yield tothe input force acting on the input member 22 in this area.

[0029] With rising input force, the force exerted by the output member24 and acting in the direction of the inlet will increase, with theproportionate force acting on the switching ring 2 rising as well. Saidproportionate force finally becomes so high that the second retainingelement 6 is lifted from stop 12 by the force applied by the switchingring 2 because the spring 5 starts to give way. Thus, the switching ring2 displaces in relation to pressure member 31 to the right in FIG. 1.This displacement continues with rising input force until the guidingprojections 15 finally come to bear against the associated end wall 11.As this occurs, the spring 5 is compressed and correspondinglyshortened. Upon further rise of the input force, the additional forcesacting on the switching ring 2 in the direction of the input are onlytaken up by the end wall 11 and, hence, by the control housing 8.Starting from this time, only surface d2 acts as a reactive force of thereaction element 7 on input member 22. The amplification of the boosterdependent on the effective surfaces is thus the result of the ratio ofsurface d4 to surface d2. An abrupt increase of the boosting effect ofthe booster is achieved by abutment of the guiding projections 15 on theend wall 11.

[0030] The operations described will be carried out in reverse directionwith declining input force. The pressure member 13 moves in relation tothe fixed switching ring 2 in FIG. 1 so far to the right until finallyspring 5 will displace the switching ring 2 to the left away from theend wall 11 by way of the second retaining element 6. Thus, theswitching ring 2 acts in the direction of the input again and transmitsa corresponding counterforce onto the input member 22 by way of spring5. As a result, the boosting ratio has decreased by an amountcorresponding to the growth of the reactive force.

[0031] The second embodiment shown in FIG. 3 is only slightly modifiedcompared to the embodiment of FIG. 1. The basic difference is thatinstead of one spring 5 two parallel connected springs 5 and 32 areused. The internally seated second spring 32 has a lower spring constantcompared to first spring 5. This way, a higher spring force that is moreprecise to proportion can be adjusted in the same space.

1. Transmission device for the brake force of a brake force booster withan elastic reaction element (7), an input member (9) acting on thereaction element (7) by way of an input effective surface, and with anoutput member (10) acting on the reaction element (7) by way of anoutput effective surface (d4), with at least part (d4-d3) of the forceexerted on the output effective surface (d4) being taken up by controlhousing (8) of the brake force booster, and with modification means(3,5,6) being provided that modify the force transmission ratio betweeninput member (9) and output member (10) defined by the ratio of theeffective surfaces (d2, d4 or d1) in dependence on the forces exerted onthe reaction element (7) by way of the effective surfaces or thedeformation of the reaction element (7) caused hereby, characterized inthat on the input side a part (d3-d2) of the surface of the reactionelement (7) is supported on the input member (9) by way of a switchingring (2) and by way of a spring element (3,5,6) and, with rising forceapplied to the reaction element (7), the switching ring (2) is displacedin opposition to the force of the spring element (3,5,6) towards a stop(11) on the control housing (8), makes catch at said and therebydecreases the input effective surface (d2).
 2. Transmission device asclaimed in claim 1, characterized in that the spring element is acaptivated spring assembly (3,5,6).
 3. Transmission device as claimed inclaim 2, characterized in that the spring assembly (3,5,6) includes aspring (5) that is compressed with bias between two movable retainingelements (3,6) which are limited in their maximum distance to each otherby a stop element (12).
 4. Transmission device as claimed in claim 3,characterized in that the first of the two retaining elements (3) bearsagainst the input member (9) and forms a projection (13) for the inputmember (9), which projection can act on the reaction element (7) andfurther includes a stop (12) that forms the stop element in relation tothe second retaining element (6).
 5. Transmission device as claimed inany one of the preceding claims, characterized in that the switchingring (2) is designed as an exchangeable loose component and, preferably,with its inside peripheral surface is guided by an external peripheralsurface (d2) of the projection (13) and/or with its external peripheralsurface (d3) is guided by the inside peripheral surface of a radialhousing projection (1) of the control housing (8) which accommodatespart (d4-d3) of the forces exerted by the reaction element (7) axiallytowards the input side.
 6. Transmission device as claimed in claim 5,characterized in that the forces from the reaction element (7) taken upby the switching ring (2) are transmitted from the second retainingelement (6) by way of spring (5) onto the first retaining element (3)until the second retaining element (6) abuts on the control housing (8).7. Transmission device as claimed in claim 6, characterized in that theforces directly introduced by the reaction element (7) in the inputdirection into the control housing (8) are transmitted onto a ring (1)fixed against the control housing (8) in the input direction. 8.Transmission device as claimed in claim 3 or any one of the followingclaims, characterized in that the second retaining element (6) includesradial second guiding projections (15) that are axially guided inassociated second guiding grooves (4) in the control housing (8), withend wall (11) of the second guiding grooves (4) forming the axial stopin the control housing (8).
 9. Transmission device as claimed in any oneof the preceding claims, characterized in that the spring element (3, 5,6, 14) includes two spiral springs (5, 14) arranged concentricallyrelative to each other.
 10. Transmission device as claimed in any one ofclaims 4 to 9, characterized in that the projection (13) is riveted tothe first retaining element (3).
 11. Transmission device as claimed inany one of the preceding claims, characterized in that said device ismounted into a controlled brake system wherein in particular thedistribution of the brake forces to the individual wheels or wheelgroups is controlled in dependence on the slip at the respective wheelor wheels.